The present invention is directed to the field of intraocular surgery. More specifically, the invention is directed to the irrigation of intraocular tissues during cataract surgery, vitrectomy surgery, and other intraocular surgical procedures. The invention provides intraocular irrigating solutions that have improved physical properties (e.g., flow characteristics) relative to prior ophthalmic irrigating solutions.
The field of intraocular surgery has advanced dramatically over the past twenty years. The advancements in this art have resulted from significant improvements in the areas of surgical techniques, surgical equipment and associated pharmaceutical products. Despite these advancements, intraocular surgery is still a very delicate process with little room for error and great potential for harm to both ocular tissues and, ultimately, the vision of the patient. Thus, there is an ongoing need to improve ophthalmic surgical techniques and equipment, as well as associated pharmaceutical products.
The present invention has resulted from an effort to improve the fluid dynamics of intraocular irrigating solutions, so as to provide greater protection for delicate intraocular tissues, while at the same time enhancing the ability of ophthalmic surgeons to perform surgical procedures more efficiently.
Although various techniques have been used previously to remove the natural crystalline lens of the eye when it becomes afflicted with a cataract, the majority of cataract surgeries today are performed by using a procedure known as “phacoemulsification”. This procedure involves the use of a surgical handpiece having a tip that vibrates at an ultrasonic frequency. The vibrating tip of the handpiece is utilized to disintegrate or “emulsify” the cataractous lens. This process necessarily generates lens fragments or particles within the eye that can cause irreparable physical damage to corneal endothelial cells if those cells are left unprotected. The corneal endothelial cells are normally protected during the phacoemulsification procedure by injecting a viscoelastic material (e.g., hyaluronic acid) into the eye to form a protective barrier over the corneal endothelial cells. However, even with the presence of the viscoelastic material, lens particles continue to move in the eye, particularly when the viscoelastic material is removed by a combined irrigating/aspiration handpiece following the phacoemulsification of the lens, prior to insertion of an artificial lens.
Due to continuous irrigation and aspiration, usually there is a lot of turbulence in the anterior chamber, within which non-aspirated lens fragments move around. In addition, the ultrasonic vibrations produced by the tip of the phacoemulsification handpiece push the lens fragments away from the tip thereby making it difficult to aspirate the fragments via the aspiration line in the tip of the handpiece. The movement of these lens fragments can cause damage to the surrounding tissue.
In addition to the lens fragments, damage may result directly from the turbulent flow of fluids intraocularly or from bubbles generated in the intraocular fluids by the phacoemulsification handpiece. Air bubbles generated during intraocular surgery have been shown to result in severe injury to the corneal endothelium in as little as twenty seconds. The turbulent flow of fluids may also cause tissue fragments to impact the delicate corneal endothelial cells or other intraocular tissues, thereby causing mechanical trauma to such tissues.
For further background regarding these problems, please refer to the following articles: Kim, et al., “Corneal endothelial damage by air bubbles during phacoemulsification”, Archives of Ophthalmology, volume 115, pages 81-88, 1997; Beesley et al., “The effects of prolonged phacoemulsification time on the corneal endothelium”, Annals of Ophthalmology, volume 18, no. 6, pages 216-219, 1986; Kondoh et al., “Quantitative measurement of the volume of air bubbles formed during ultrasonic vibration”, Folia Ophthalmogica Japan, volume 45, no. 7, pages 718-720, 1994 and Kim et al., Investigative Ophthalmology & Visual Science, volume 37, no. 3, S84, 1996.
The fluid dynamics of intraocular irrigating solutions is also important during vitrectomy procedures and various other types of intraocular surgical procedures. Turbulence in intraocular fluids may also result from the movements of reciprocating vitrectomy handpieces, the alternating vacuum and irrigation modes of irrigation/aspiration handpieces and movements of other surgical handpieces and devices utilized in such procedures. The elimination or reduction of such turbulence helps to protect the retina and other tissues located in the posterior segment of the eye, as well as tissues located in the anterior segment of the eye, such as the corneal endothelial cells.
In view of these potential complications, there is a need for intraocular irrigating solutions having improved physical properties that: (1) reduce the potential for turbulence within the anterior and posterior chambers of the eye, (2) help to contain the movement of tissue fragments and air bubbles within the eye, and (3) facilitate the removal of lens fragments and other tissue fragments by making it easier for the surgeon to track the fragments with the tip of the surgical handpiece. The present invention is directed to fulfilling this need. Specifically, the present invention is directed to the provision of an irrigating solution that provides for greater control of the movement of tissue fragments, air bubbles and other particles during phacoemulsification, vitrectomy and other intraocular surgical procedures. This control of particle movement is fundamentally different from the above-discussed use of a layer of viscoelastic material to protect the corneal endothelial cells by means of a cushioning effect. The irrigating solution of the present invention is designed to provide a protective effect beyond that obtained by means of viscoelastic agents.